Eye disorders are treated by ophthalmologists or optometrists. Ophthalmologists are physicians and surgeons who specialize in the diagnosis and treatment of eye diseases. Optometrists are not physicians but have a doctor of optometry degree and do eye examinations, prescribe corrective lenses and prescribe drugs for certain types of eye disorders. Opticians are technicians who can fit eyeglasses and contact lenses using prescriptions provided by an ophthalmologist or optometrist. Opticians do not diagnose or treat eye diseases.

Each part of the eye has a unique function. Light enters the eye through the cornea, the clear, curved layer in front of the iris and pupil. After passing through the cornea, light travels through the pupil (the black dot in the middle of the eye). The pupil is actually an opening in the middle of the iris—the circular, colored area of the eye. Muscles that attach to the iris open and close the pupil to control the amount of light that enters the eye. Behind the iris sits the lens. By changing its shape, the lens focuses light onto the retina, a layer of tissue at the back of the eye. The retina contains the cells that sense light (photoreceptors). Each photoreceptor converts light into an electrical signal that is transmitted to the brain through a bundle of nerve fibers called the optic nerve.

Eye DisordersSections (A-Z)

Biology of the Eyes

The structures and functions of the eyes are complex. Each eye constantly adjusts the amount of light it lets in, focuses on objects near and far, and produces continuous images that are instantly transmitted to the brain.

Cataract

Conjunctival and Scleral Disorders

The conjunctiva is the membrane that lines the eyelid and loops back to cover the sclera (the tough white fiber layer covering the eye), right up to the edge of the cornea (the clear layer in front of the iris and pupil—see Structure and Function of the Eyes ). The conjunctiva helps protect the eye by keeping small foreign objects and infection-causing microorganisms out and by contributing to the maintenance of the tear film.

Corneal Disorders

The cornea is the clear layer in front of the iris and pupil. It protects the iris and lens and helps focus light on the retina. It is composed of cells, protein, and fluid. The cornea looks fragile but is almost as stiff as a fingernail. However, it is very sensitive to touch.

Diagnosis of Eye Disorders

A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2 years or more frequently if there is an eye condition) by an ophthalmologist or an optometrist. An ophthalmologist is a medical doctor who specializes in the evaluation and treatment (surgical and nonsurgical) of eye disorders. An optometrist is a health care practitioner who specializes in the diagnosis and treatment of vision or refractive problems (refractive errors).

Eye Socket Disorders

The eye sockets (orbits) are bony cavities that contain and protect the eyes and their supporting structures (see Figure: An Inside Look at the Eye and see Figure: Structures That Protect the Eye ). Disorders affecting the orbits include

Eyelid and Tearing Disorders

The eyelids play a key role in protecting the eyes. They sweep away debris when the eyes close and help spread moisture (tears) over the surface of the eyes when they open. The eyelids provide a mechanical barrier against injury by closing rapidly when needed.

Glaucoma

Optic Nerve Disorders

The small photoreceptor cells of the retina (the inner surface at the back of the eye) sense light and transmit impulses to the optic nerve. The optic nerve from each eye carries impulses to the brain, where visual information is interpreted.

Refractive Disorders

Retinal Disorders

The retina is the transparent, light-sensitive structure at the back of the eye. The cornea and lens focus light onto the retina. The central area of the retina, called the macula, contains a high density of color-sensitive photoreceptor (light-sensing) cells. These cells, called cones, produce the sharpest visual images and are responsible for central and color vision. The peripheral area of the retina, which surrounds the macula, contains photoreceptor cells called rods, which respond to lower light levels but are not color sensitive. The rods are responsible for peripheral vision and night vision.

Symptoms of Eye Disorders

A person may experience swelling in one or both eyelids. Swelling may be painless or accompanied by itching or pain. Eyelid swelling is distinct from bulging eyes , although a few disorders can cause both.

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